We all saw firsthand how quickly a disease you've never heard of in a place you may have never been can become a public health emergency right in your own backyard. Viruses like COVID-19 remind us that, for all our differences, everyone in this world is connected biologically by a microscopic network of germs and particles – and that, like it or not, we're all in this together. We hope the experience we've all lived through over the last year will lead to a long-term change in the way people think about global health – and help people in rich countries see that investments in global health benefit not only low-income countries but everyone. We were thrilled to see the United States include $4 billion for Gavi in its latest COVID-19 relief package. Investments like these will put all of us in a better position to defeat the next set of global challenges.

Just as World War II was the defining event for our parents' generation, the coronavirus pandemic we are living through right now will define ours. And just as World War II led to greater cooperation between countries to protect the peace and prioritize the common good, we think that the world has an important opportunity to turn the hard-won lessons of this pandemic into a healthier, more equal future for all.In the rest of this letter, we write about two areas we see as essential to building that better future: prioritizing equity and getting ready for the next pandemic.

Can we emerge from this pandemic more equal than we entered it?

Melinda: One of the things I've missed most over the last year is traveling to see our foundation's work in action. I have photos all over our house of the women I've met on these trips. Now that I'm working from home, I see their faces all the time.

I often wonder what the pandemic looks like through their eyes and how they're coping. When I'm on videocalls with experts and world leaders, I try to imagine how the decisions being made in these conversations will affect these women and their families. They're a daily reminder of the importance of ensuring that the world's COVID-19 response leaves no one behind.

From AIDS to Zika to Ebola, disease outbreaks tend to follow a grim pattern. They hurt some people more than others – and who they hurt most is not random. As they infect societies, they exploit pre-existing inequalities.

The same is true of COVID-19. People with less are faring worse than those with more. Essential workers are facing greater risks than those who can work from home. Students without internet access are falling behind students who are learning remotely. In the United States, communities of color are more likely to get sick and die than other Americans. And all around the world, women who have been fighting for power and influence over their lives are seeing decades of fragile progress shattered in a matter of months.

From the beginning of the pandemic, our foundation has worked with partners in the United States and around the world to address the uneven social and economic impacts of COVID-19 and keep those pre-existing inequalities from growing deeper.

In the United States, many of our anti-COVID efforts overlap with our work on racial equity. For example, the data tell us that Black Americans are three times as likely as white Americans to get COVID-19, and they are also more likely to live in an area with limited access to COVID-19 testing. To help meet the demand for local community testing, our foundation partnered with historically Black colleges and universities to expand diagnostic testing capacity on their campuses.

We're also addressing the pandemic's disproportionate impact on people of color in other ways, including through our foundation's U.S. education work. We're concerned about students falling behind at all levels (when schools closed last spring, the average student lost months of learning), but we're especially troubled that COVID-19 could exacerbate long-standing barriers to higher education, particularly for students who are Black, Latino, or from low-income households. Median lifetime earnings of college graduates are twice those of high school graduates, so the stakes for these young people are high. To help students navigate COVID-19 roadblocks, our foundation expanded our partnerships with three organizations that have a proven track record of using digital tools to help students stay on the path to a college degree. We think the models and approaches these organizations are honing now will continue to expand opportunities for students post-pandemic, too.

When it comes to our work outside the United States, my major focus has been calling on world leaders to put women at the center of their COVID-19 response. If governments ignore the fact that the pandemic and resulting recession are affecting women differently, it will prolong the crisis and slow economic recovery for everyone.

For example, because of the economic shutdowns over the last year, hundreds of millions of people in low-income countries have needed help from their government to meet basic needs. But the cruel irony is that the women who most need these economic lifelines tend to be invisible to their governments. It's hard to send cash safely and swiftly to a woman who doesn't appear in the tax rolls, have a formal identification, or own a mobile phone. Unless financial systems are specifically designed to include these women, these systems are likely to exclude them, pushing them even further to the economic margins. Our foundation has worked with the World Bank to help countries overcome these hurdles and create digital cash transfer programs with women's needs in mind.

More broadly, we're supporting efforts to design economic response plans targeted at women and low-wage workers. In low- and middle-income countries, the poorest people tend to be self-employed in the informal sector – as farmers or street vendors, for example. Policymakers often overlook these workers, and traditional stimulus measures don't meet their needs. (Tax rebates don't really help people who don't pay taxes – and who pays for your paid leave if you work for yourself?) Our foundation helped fund research into how governments can repair these holes in the safety net by prioritizing measures like cash grants, food relief, and moratoriums on rent and utilities.

This past year has also shined a spotlight on women's unpaid labor, an issue I've written about in this letter before. With billions of people now staying home, the demand for unpaid care work – cooking, cleaning, and childcare – has surged. Women already did about three-quarters of that work. Now, in the pandemic, they've taken on even more of it. This work may be unpaid, but it comes at an enormous cost: Globally, a two-hour increase in women's unpaid care work is correlated with a 10 percentage point decrease in women's labor force participation. As governments rebuild their economies, it's time to start treating child care as essential infrastructure – just as worthy of funding as roads and fiber optic cables. In the long term, this will help create more productive and inclusive post-pandemic economies.

Bill and I are deeply concerned, though, that in addition to shining a light on so many old injustices, the pandemic will unleash a new one: immunity inequality, a future where the wealthiest people have access to a COVID-19 vaccine, while the rest of the world doesn't.

Already, wealthy nations have spent months prepurchasing doses of vaccine to start immunizing their people the moment those vaccines are approved. But as things stand now, low- and middle-income countries will only be able to cover about one out of five people who live there over the next year. In a world where global health is local, that should concern all of us. From the beginning of the pandemic, we have urged wealthy nations to remember that COVID-19 anywhere is a threat everywhere. Until vaccines reach everyone, new clusters of disease will keep popping up. Those clusters will grow and spread. Schools and offices will shut down again. The cycle of inequality will continue. Everything depends on whether the world comes together to ensure that the lifesaving science developed in 2020 saves as many lives as possible in 2021.

Existential crises such as these leave no facet of life untouched. But solutions that are worthy of these historic moments also have ripples. Demanding an inclusive response will save lives and livelihoods now – and create a foundation for a post-pandemic world that is stronger, more equal, and more resilient.

It's not too soon to start thinking about the next pandemic.

Bill: One of the questions I get asked the most is when I think the world will get back to normal. I understand why. We all want to return to the way things were before COVID-19. But there's one area where I hope we never go back: our complacency about pandemics.

The unfortunate reality is that COVID-19 might not be the last pandemic. We don't know when the next one will strike, or whether it will be a flu, a coronavirus, or some new disease we've never seen before. But what we do know is that we can't afford to be caught flat-footed again. The threat of the next pandemic will always be hanging over our heads – unless the world takes steps to prevent it.

The good news is that we can get ahead of infectious disease outbreaks. Although the world failed to prepare for COVID-19 in many ways, we're still benefiting from actions taken in response to past outbreaks. For example, the Ebola epidemic made it clear that we needed to accelerate the development of new vaccines. So, our foundation partnered with governments and other funders to create the Coalition for Epidemic Preparedness Innovations. CEPI helped fund a number of COVID-19 candidates – including the Moderna and Oxford AstraZeneca vaccines – and is deeply involved in the vaccine equity work that Melinda wrote about.